Waders, waders, waders

Research recently published in the Journal of Applied Ecology shows that the shrinking of mudflats along the coasts of the Chinese Yellow Sea is an increasing problem for migratory birds that travel between Siberia and Australia.   This research, led by Theunis Piersma, shows that three wader species, the Knot, Great Knot and Bar-tailed Godwit, are in decline because of one common factor: loss of food and habitat along the coasts of the Yellow Sea.  During our work at Chongming Dongtan we have been privileged to work not only with David Melville, but also Professor Ma of Fudan University, two members of the research team. 

Chongming Island, at the mouth of the Yangstze is a remarkable place for waders.  However, we have witnessed the remarkable speed of the loss of intertidal areas along the coast through reclamation, and also the threats, such as wind farms and shell-fisheries on the remaining areas.  The photographs here show some of the research, the threats and the diversity of waders that occur on this coast.

 (Bar-tailed Godits and pumping dredgings - David Melville)

 Great Knot 

 Red-necked Stint

 Wind farms, shell-fishing and waders

 Mudflat reclamation

 Marsh sandpiper

 Spoony

Whimbrel

Broad-billed Sandpiper

Collecting clams

 Long-billed Dowitcher

Sharp-tailed Sandpiper

Hooded Cranes

Chongming Dongtan is one of the most important wintering sites in China for Hooded Cranes, with the majority of the population wintering in Japan at one site, Izumi.  It is a threatened and declining species with a global population of around 11,000 birds.  At Chongming Dongtan, it winters primarily on the saltmarsh.  Sea Bulrush Scirpus mariqueter is a dominant species in the saltmarsh vegetation; and its corms and seeds form a major food source for the cranes (and other wintering waterbirds such as Tundra Swan).  One study showed that the corms and rhizomes composed about 99% of the total food content of the cranes.  

The corms in the outer saltmarsh zone (far from the seawall) are easier to find by the cranes as they are buried underground shallower than those in the inner zone due to daily erosion by tidewater. So, for easy access to food, Hooded Crane tended to select the regions near the channels at low tide as their foraging habitat.  Despite the similar food content between Hooded Crane and Tundra Swan, obvious ecological separation occurs in their foraging behaviour, foraging times and foraging habitats.  

However, the native Scirpus mariqueter dominated tidal vegetation is highly threatened and diminishing rapidly.   Land reclamation is a major threat all along the Chinese coast but the native vegetation is also being out-competed by the non-native Smooth Cord-grass Spartina alterniflora  (the eradication of which is the focus of our project at Chongming).  Human activities such as fishing, and notably eel fishing at Chongming Dongtan, have resulted in serious disturbance to the Hooded Crane and other waterbirds.  Although the cranes continue to focus their activity on the remaining good quality saltmarsh, they now also increasingly feed in rice paddies just over the sea wall, particularly at high tide.  One of the reserve projects at Chongming is to create ‘sacrificial’ rice paddies in safe locations for the benefit of the cranes and other waterbirds.

We found a mixed flock of 70 Hooded and 18 Common Cranes loafing and displaying on the upper areas of the saltmarsh.  Interestingly, there was one family of apparent hybrid Hooded x Common Cranes, a not infrequent occurrence.  These birds displayed the bulk and general colour of the Commons but had a washed-out Hooded head pattern.

Pics- above: Hooded Cranes (with Common Crane in the background).

Below: cranes on the salt marsh with distant fishing boats and bouys, displaying Hooded and Common Cranes with some hybrids in the foreground.